The use of heat transfer fluids for cooling or heating or thermally regulating components (e.g., microelectronics, optoelectronics, etc.) has become increasingly important for a wide range of industries and applications, including manufacturing, transportation and military operations. Given the increasing importance of heat transfer fluids, there is further a need for improving the thermal conductivity of such fluids so as to enhance the thermal properties and performance of these fluids for particular applications.
One approach to enhancing the thermal conductivity of heat transfer fluids is by adding solid particles to fluids, a well-known technique that has been investigated for at least the last several decades. Numerous theoretical and experimental studies have been conducted in relation to thermal properties of heat transfer fluids including solid particles or fibers. See, e.g., the following published documents, all of which are incorporated herein by reference in their entireties: S. U. S. Choi, Developments and Applications of Non-Newtonian Flows, edited by D. A. Siginer and H. P. Wang (ASME, New York, 1995), p. 99; J. A. Eastman, S. U. S. Choi, S. Li, et al., Applied Physics Letters 78, 718 (2001); S. U. S. Choi, Z. G. Zhang, W. Yu, et al., Applied Physics Letters 79, 2252 (2001); S. K. Das, N. Putra, P. Thiesen, et al., Transactions of the ASME. Journal of Heat Transfer 125, 567 (2003); H. E. Patel, S. K. Das, T. Sundararajan, et al., Applied Physics Letters 83, 2931 (2003); D. H. Kumar, H. E. Patel, V. R. R. Kumar, et al., Physical Review Letters 93, 144301/1 (2004); and R. Prasher, P. Bhattacharya, and P. E. Phelan, Physical Review Letters 94, 025901/1 (2005). The early studies into such heat transfer fluid systems have been limited to fluids containing solid particles on the order of millimeters or micrometers (microns) in size or dimension. However, one problem associated with such fluids is that the particles tend to settle out of the solutions. Another problem is that the solid particles can become lodged or can clog microchannels of equipment in which the heat transfer fluid flows.
Recent advances in heat transfer fluids involve the use of solid nanoparticles, or particles having dimensions in the range of 1 nm to 100 nm, in heat transfer fluids (also referred to as “nanofluids”). The nanofluids do not suffer from the problems noted above for heat transfer fluids utilizing larger sized solid particles. In addition, such nanofluids have been demonstrated to have enhanced thermal conductivity. For example, one study has shown that the dispersion of copper nanoparticles within ethylene glycol results in an increase in thermal conductivity by about 40% for volume fractions of about 0.3%. See J. A. Eastman, S. U. S. Choi, S. Li, et al., Applied Physics Letters 78, 718 (2001).
However, there remains a question regarding the ability to effectively mass-produce nanofluids (i.e., heat transfer fluids containing nano-sized solid particles). In addition, there is a concern regarding the long-term stability of nanofluids. In view of these concerns, the use of current nanofluids in different industries and applications has been somewhat limited.
Accordingly, a need exists for providing heat transfer fluids with enhanced thermal conductivities and other thermal properties and which are stable and reliable for use for a wide variety of different applications.